The invention relates to a method for determining the transit time of electrical signals on printed circuit boards, in particular printed circuit boards which can be equipped with memory chips such as SDRAMs, using time domain reflection measurement (TDR measurement) and automatic standard test equipment.
The usually unknown transit times of electrical signals on printed circuit boards or PCBs have hitherto been simulated in computers. After the mounting of the circuit board, the transit times can be determined experimentally using time domain reflection measurement by a unit that is specially produced for this purpose.
In automatic standard test equipment (ATE), the time domain reflection measurements are typically used in order to determine transit times on the performance board associated with the ATE, which transit times are then taken into account as offset parameters. When the transit times are standardized during production, it is conventional practice not to determine or take into account transit times on the printed circuit boards PCB of, for example, SDRAM modules.
It is accordingly an object of the invention to provide a method for determining the transit time of electrical signals on printed circuit boards using automatic standard test equipment which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type, in which usually unknown transit times of electrical signals on printed circuit boards (PCBs) are determined per channel using automatic standard test equipment in order to optimize test parameters and increase the precision of tests to be carried out.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for determining transit times of electrical signals on printed circuit boards using a time domain reflection measurement technique. The method includes measuring a first signal transit time of a first signal travelling from a starting point to a fitting of a specific plug-in slot on a standard performance board of an automatic test equipment unit. The standard performance board is configured without a printed circuit board being plugged in the fitting. The printed circuit board is then inserted into the fitting of the plug-in slot of the standard performance board. A second signal transit time of a second signal travelling from the starting point to an end point along at least one channel on the printed circuit board plugged in, is measured. A difference between the first signal transit time and the second signal transit time is derived, and from the difference, a channel signal transit time of the channel on the printed circuit board is determined.
Using automatic standard test equipment (ATE) and the standard routines made available in it for determining transit times on the performance board associated with the ATE, it is possible, with the method according to the invention, to determine the transit times on the printed circuit board per channel. By using productively employed equipment, all the fault sources that occur during a transfer from an additional piece of test equipment are eliminated.
The transit time measurement is preferably carried out with a partially equipped printed circuit board, that is to say with the entire module without active components such as SDRAMs, PLL or registers, but with all the passive components such as resistors and capacitors.
The transit time measurement of the printed circuit board is preferably carried out for all the channels, that is to say all the signal pins of the printed circuit board. By the formation of a difference between the measured (first) transit time and the measured sum of the transit times (the second transit time), the influence of the printed circuit board becomes clearly apparent.
The invention thus makes it possible for the performance of the fully operationally capable printed circuit board which is equipped with all the components, that is to say of the entire module, to be separated quickly and unambiguously from the influence of the transit time of the printed circuit board. As a result, the test parameters can be optimized and the precision of the tests increased.
The advantage of the present method for determining the transit time is the precise determination of the transit times for each channel on a printed circuit board using automatic standard test equipment ATE and standard performance boards which are used in standard module testing technology.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for determining the transit time of electrical signals on printed circuit boards using automatic standard test equipment, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.